1. Field of the Invention
The present invention relates to a method of producing an ester compound.
More particularly, the present invention relates to a method of producing an ester compound, in which method a chloroformic acid alkyl ester is decomposed into a corresponding alkyl chloride and simultaneously a content of hydrogen chloride or chlorine is reduced. The method of the present invention is useful to produce an ester compound and refine various mixed gases containing a chloroformic acid alkyl ester and hydrogen chloride or chlorine in various concentrations, by bringing the chloroformic acid alkyl ester-containing gas into contact with a specific catalyst and thereby converting the chloroformic acid alkyl ester to an alkyl chloride, and simultuneously reducing the content of hydrogen chloride or chlorine and removing the alkyl chloride from the mixed gas.
The method of-the present invention is applicable to production of a mixed gas from a gas phase catalytic carbonylation reaction of carbon monoxide with at least a nitrous acid ester in the presence of a solid catalyst and a chlorine-containing substance, and containing, as a by-product, a chloroformic acid alkyl ester in addition to the resultant carbonylation product, for example, dialkyl carbonate or dialkyl succinate. The method of the present invention can contribute to preventing corrosion in a refining apparatus due to the chloroformic acid alkyl ester contained in the gas mixture.
2. Description of Related Art
As a known method of decomposing a chloroformic acid ester J. Am. Chem. Soc., 77, 5033 (1955) discloses a method of converting a chloroformic acid ester to an alkyl chloride by heating the chloroformic acid ester in the presence of a Lewis acid such as boron trifluoride. This method is disadvantageous in that a long time is necessary for the decomposition of a lower alcohol ester of chloroformic acid and the resultant degree of decomposition is low.
Also, German Unexamined Patent Publication (DE-OS) No. 2,545,659 discloses a method of producing an alkyl chloride by heating a chloroformic acid ester at a temperature of 120.degree. to 130.degree. C. in an aprotic solvent, for example, N-methylpyrrolidone. This method is disadvantageous in that this is a liquid phase method in which a special solvent must be employed and a solvent vessel must be provided, and thus is not economical for industrially decomposing the chloroformic acid ester.
U.S. Pat. No. 4,260,810 and U.S. Pat. No. 5,162,563 disclose that in catalytic carbonylation reactions, for example, in carbonic acid ester-synthesis reactions or dicarboxylic acid diester-synthesis reactions, of carbon monoxide with at least nitrous acid esters in a gas phase in the presence of a solid catalyst comprising a platinum group metal chloride carried on a carrier, the catalytic activity of the solid catalyst gradually decreases during the reaction, and in the industrial procedure, a small amount of a chlorine-containing substance, for example, hydrogen chloride, chlorine or a chloroformic acid ester, is continuously fed into the reaction system to prolong the durability of the catalyst and to maintain its selectivity for the targeted compound at a desired level or to enhance its selectivity.
In the above-mentioned carbonylation reaction procedures, the resultant reaction product mixture produced in the reaction system contains a small amount of a chloroformic acid alkyl ester derived from hydrogen chloride or chlorine added to the reaction system or a small amount of a chloroformic acid alkyl ester, hydrogen chloride or chlorine added to the reaction system, in addition to the aimed reaction product, for example, a carbonic acid ester or dicarboxylic acid diester, non-reacted fractions of carbon monoxide and nitrous acid ester, and another additive, for example, nitrogen monoxide and nitrogen, and therefore, the chloroformic acid alkyl ester and hydrogen chloride or chlorine is brought together with the targeted ester compound into a collecting and refining process for the targeted ester compound. Where the chloroformic acid alkyl ester, which has a poor resistance to hydrolysis or alcoholysis, is introduced into the collecting and refining process, the chloroformic acid alkyl ester is decomposed to a corresponding corrosive chlorine-containing substance, for example, hydrogen chloride, and the corrosive chlorine-containing substance contaminates the targeted product and corrodes the apparatus. Therefore, in this case, it is required to further refine the product to remove the corrosive chlorine-containing substance, or to make the refining process apparatus by a specific material having a high resistance to the corrosive chlorine-containing substance. Namely, the corrosive chlorine-containing substance contained in an industrial product causes significant disadvantages in cost and/or production efficiency.
Nevertheless, with respect to the carbonylation reaction product containing a small amount of a chloroformic acid alkyl ester, it has, until now, not been known how to decompose it to a substantially non-corrosive substance with a high economical efficiency.
Accordingly, there is a strong demand for a method of decomposing chloroformic acid alkyl esters to a substantially non-corrosive substance and reducing the content of corrosive chlorine-containing substance efficiently and economically, which method is useful, for example, for refining a reaction product mixture derived from carbonylation reactions of carbon monoxide with at least a nitrous acid ester.